1. Field of the Invention
The present invention relates to a thin-film magnetic head for writing data on a magnetic recording medium with high coercive force to stabilize the magnetization thermally, a head gimbal assembly (HGA) having this thin-film magnetic head and a magnetic recording/reproducing apparatus having this HGA. Further, the present invention relates to a magnetic recording method for writing data on such a magnetic recording medium with high coercive force.
2. Description of the Related Art
Further improvement of the performance and characteristic of thin-film magnetic heads and magnetic recording media has been demanded with acceleration of the recording density of magnetic recording/reproducing apparatuses represented by magnetic disk drive apparatuses. As the thin-film magnetic head, used is a composite type thin-film magnetic head in which a magnetoresistive (MR) effect element as a read head element for reading data and an electromagnetic coil element as a write head element for writing data are stacked. Currently, in this head, the reduction in size of the both head elements by applying microfabrication, and the improvement of characteristics thereof by applying new material system has been intended.
On the other hand, the magnetic recording medium is composed of a magnetic particle assembly, and generally, one record bit is constituted of a plurality of the magnetic particles. In order to intensify the recording density by reducing a magnetic fluctuation in borders of the record bits, further miniaturization of the magnetic particles has been conventionally tried. However, the more the magnetic particle is miniaturized, the more a heat fluctuation is generated in the magnetic particle due to the reduction in volume of the particle, thereby degrading thermal stability of the magnetization.
As a measure to cope with this problem, currently, the transition from longitudinal magnetic recording system to perpendicular magnetic recording system has been considered and realized in actual products. In the perpendicular magnetic recording medium, the heat fluctuation can be suppressed more easily by securing a predetermined magnetic recording layer thickness despite the miniaturization of the magnetic particles, compared with a longitudinal magnetic recording medium. Consequently, the surface recording density can be improved largely.
However, to further improve the recording density, required is further miniaturization of the magnetic particles that constitute the perpendicular magnetic recording medium and the secure suppression of the heat fluctuation. Thus, increasing magnetic anisotropy energy of the magnetic particles may be considered as the measure. However, the increase in the magnetic anisotropy energy causes the increase in coercive force of the magnetic recording layer. Actually, the coercive force of the magnetic recording layer intended to suppress the heat fluctuation is more than 5 kOe (400 kA/m). On the other hand, the write field intensity of the magnetic head is determined mainly by the saturation magnetic flux density of a soft-magnetic material that constitutes poles in the head, so that a saturated magnetic recording, which requires a write field intensity of about 2 times higher than the coercive force, is difficult to be implemented.
As another measure, there has been proposed a heat-assisted magnetic recording system in which a writing is performed to a magnetic recording medium with coercive force reduced by heating just before the write field is applied, while using the magnetic recording layer with high coercive force (that is, with large magnetic anisotropy energy Ku).
As a method for heating the magnetic recording medium in the heat-assisted magnetic recording system, currently, an irradiation electron beam or near-field light to the magnetic recording medium has been mainly proposed. For example, according to Japanese Patent Publication No. 2001-250201A, electrons are irradiated to the magnetic recording medium using an electron discharge source. The irradiation causes the recording portion of the magnetic recording medium to be heated and rise in temperature. As a result, the coercive force is lowered and the magnetic information can be recorded by the magnetic recording head. Further, Japanese Patent Publication No. 2004-158067A discloses a technology in which a scattering body that constitutes a near-field light probe and is provided adjacent to a main magnetic pole of the perpendicular magnetic recording head is irradiated with laser beam by using a semiconductor laser device provided in the head. By using the technology, near-field light is generated, and the near-field light is irradiated to the magnetic recording medium. As a result, the magnetic recording medium is heated and rises in temperature.
However, such heat-assisted magnetic recording system contains a variety of difficulties in terms of technology, which is a problem to be solved.
To actually realize the thin-film magnetic head for heat-assisted magnetic recording described above, generally, a minute electron discharge source, a laser light source or an optical component with high positioning accuracy and dimensional accuracy is needed to be formed inside the head, which becomes a large burden for the manufacturing process. As a result, this can bring increase in the manufacturing cost. Further, the structure is complicated by providing new devices such as the electron discharge source, the laser beam source or the optical component, thereby disabling the head to be compact, which is a demand for the commercial product.
In the structure of the general thin-film magnetic head, in which an element formation surface and an opposed-to-medium surface are perpendicular to each other, it is quite difficult in terms of design to dispose the electron discharge source so that electrons are discharged from the opposed-to-medium surface or to dispose the laser light source so that the light beam becomes parallel to the element formation surface. For the reason, it becomes difficult to irradiate electrons or near-field light accurately to a record position of the magnetic recording layer, then to apply write field thereon.
In the heat-assisted magnetic recording system, not only the record position but also neighborhood thereof is heated by heat conduction. Thus, the heat fluctuation of the magnetic particles may be even more accelerated. Further, because the temperature distribution of heated portions or the write field distribution of the magnetic head are not uniform, it is difficult to magnetically reverse or demagnetize only desired record positions. Consequently, it becomes difficult to write data with high accuracy and high quality.
Further, it is preferable to use a material having a large reduction rate of the coercive force along with temperature increase as the material of the magnetic recording layer in order to lower the coercive force temporarily by heating. However, the development of such new material can be a large burden, and in the developed new material, the heat fluctuation may be increased along with increase in ambient temperature.